1) Field of the Invention
The present invention relates to an erasing method of erasing a recording agent on a recording surface of a recording medium recorded by a recording agent composed of a near IR erasable dye, for example, an aqueous ink, an oily ink, toner, etc., and an erasing apparatus for performing that erasing method.
2) Description of the Related Art
In recent years, near IR erasable dyes have been coming under attention as dyes of the recording paper used in various printers, copying machines, etc. This is because a repeated reuse of the recording medium such as recording paper recorded by such a recording agent is possible, and this can contribute to the conservation of forest resources. As disclosed in for example Japanese Unexamined Patent Publication (Kokai) No. 4-362935, a near IR erasable dye is a complex compound of a near IR absorbing cationic dye-boron anion. This compound is decomposed by irradiation of near infrared rays (a wavelength of 700 nm or more) to become a transparent substance, but is a relatively stable compound under visible rays. Accordingly, it is possible to utilize the near IR erasable dye as a recording agent in various printers etc., for example, various dyes of inks and toners, whereby the recording agent on the recording paper can be decomposed and erased by the irradiation of the near infrared rays, therefore making reuse of the recording paper possible.
So as to achieve an enhancement of the efficiency of reuse of recording paper, it is necessary to quickly and effectively carry out processing for decomposition of the near IR erasable dye, that is, processing for erasing of the recording agent. The decomposition of the near IR erasable dye is promoted under the presence of an appropriate catalyst, for example, tetrabutyl ammonium butyl triphenyl borate. In the above-mentioned Japanese Unexamined Patent Publication (Kokai) No. 4-362935, as the recording agent composed of the near IR erasable dye and the catalyst (sensitizing agent), an ink or a toner has been proposed, and such a near IR erasable dye included in the recording agent is smoothly decomposed due to such a catalyst at the time of irradiation of near infrared rays, therefore a quick erasing processing of the recording agent, that is, an enhancement of efficiency of reuse of. the recording paper, can be achieved.
Also, natural light or room light includes light having a wavelength of 700 nm or more, therefore where the recording paper recorded by a catalyst-containing recording agent is left to stand for a long period, the recording density on the recording paper, that is, the printing density, is gradually lowered due to the catalyst. Therefore, arises a problem on the point of persistency of such a recording paper. Moreover, it is pointed out that there is a problem that, where the printing density is once lowered in this way, even if the irradiation of near infrared rays is positively carried out to that recording agent, complete erasure cannot be carried out.
On the other hand, it is known also that the erasability of the recording agent as mentioned above is promoted under a high temperature, and therefore it is also proposed that the recording paper be heated at the time of erasing and that subsequently irradiation of the near infrared rays be carried out. In this case, both of the heating source for heating the recording paper and the near IR irradiation source become necessary. It goes without saying that the provision of both of the heating source and the near IR irradiation source leads to the result of an increase of production costs of the erasing apparatus.